The present invention relates to an optical device module used in an optical receptacle type optical transceiver, such as a light-emitting device module or a light-receiving device module, and also to an optical transceiver of light receptacle structure in which the above-mentioned optical device module is mounted.
With the increase in the amount of transmission in recent years due to the diffusion of the Internet, for example, optical transceivers have come to be used as articles of everyday use. As for the mode of using optical transceivers in this case, it is most effective to use optical receptacle type optical transceivers, which can be directly detached and connected to the panel of a router or a switch, for example, to which the optical connector can be directly connected. In other words, the optical transceivers of this type are superior in maintainability and expandability. Moreover, there is strong requirement that optical transceivers should provide characteristics as general-purpose devices, which include better EMC characteristics and desirable optical connection characteristics in handling the optical connector.
FIG. 4 shows the structure of a light-emitting device module or light-receiving device module for a conventional optical receptacle. A stub ferrule 403 is contacted to an optical-connector ferrule by the spring force of the optical connector part in the receptacle, not shown, and guides a laser beam into an optical fiber. As the leading end portion of the stub ferrule 403 is aligned to the optical-connector ferrule by a sleeve 402, light is coupled into a single mode fiber about 10 μm in diameter.
After the stub ferrule 403 is press-fit into a metal-made holder 404 and a sleeve 402 is mounted, a metal-made sleeve cover 401 is fixed by being press-fit to the metal-made holder 404 from the outside. The parts 401, 402, 403 and 404, which have been put together and which have been centered with respect to a light-emitting device or a light-receiving device 406, are connected together by YAG welding.
In order that the stub ferrule 403 and the sleeve 402 can attain a high connection characteristic of an optical connector which requires a μm-level accuracy, they are often made of a ceramic superior in hardness and machining accuracy. In addition a reference numeral 407 denotes a lens, and 409 denotes a stem.
In the structure of a light-emitting device module or light-receiving device module for a conventional optical receptacle, in an optical transceiver which adopts this kind of module, problems described below are likely to occur.
(1) In a light-emitting device module or a light-receiving device module, a light-emitting device or a light-receiving element 408 which operates at high speed is mounted, and the light-emitting device is driven by a modulated relatively large current (several tens of mA, for example) and the light-receiving device deals with a minute modulated current signal (several tens of μA, for example) obtained as a result of photoelectric conversion. If the sleeve cover 401 at the leading end portion of the light-emitting device module or the light-receiving element is made of metal, this metal portion may act as a radiating antenna or receiving antenna. As a result, EMI and EMS characteristics deteriorate.
(2) When a statically charged person touches an optical connector connected to an optical transceiver, if the sleeve cover 401 at the leading end portion of the light-emitting device module or light-receiving device module is a metal piece, the static electricity released from the human body conducts through a metal spring in the optical connector and the optical ferrule metal-made retainer and is discharged to the metal sleeve cover 401 at the leading end portion of the light-emitting device module or the light-receiving device module which comes close to the optical connector when optical connector is connected. This discharged static electricity flows through the metal-made holder 404 and the metal-made adapter 405, causing a malfunction to occur in an internal circuit, including the light-emitting device or the light-receiving element 408.
To improve those problems, in a technology disclosed in JP-A-2001-66468, a method of using a resin material for the sleeve cover is adopted. However, because the resin material is inferior in hardness than a metal material, when a stress, which corresponds to a transversal tensile force to the optical fiber, is applied to the optical connector under the condition that the optical connector is connected to an optical receptacle type optical transceiver, that resin portion itself is deformed by the stress, thus increasing the optical connection loss.
In recent years, besides maintenance personnel skilled in this special field, an increasing number of general users handle optical fibers, and there has been higher demand for optical connection characteristics and resistance characteristics in handling optical fibers, which is undesirable.
In the case where the sleeve or the sleeve holder is made of a resin, when the optical connector is disconnected or connected, it sometimes occurs that the optical-connector ferrule, which is generally made of a hard substance, at the end of the optical connector contacts the resin sleeve or sleeve holder and scrapes the surface, with the result that scraping chips of the resin material are produced. The scraping chips enter between the contact surfaces of the optical-connector ferrule and the stub ferrule of the light-emitting device module or light-receiving device module, involved in coupling of light, giving rise to an increase in optical connection loss at the contact surfaces and deteriorations in optical connection characteristics, such as an increase in reflected light.
Furthermore, in the connection between an optical fiber cable and an optical transceiver or an optical transmitter or an optical receiver, light is coupled by contact between an optical connector on the optical fiber cable side and an optical receptacle with which the optical connector is connected on the optical transmitter/receiver side.
The structure of a conventional optical receptacle is such that the stub ferrule is split and enclosed by a sleeve and those parts are fixed with two parts, a sleeve cover and a holder, by YAG welding, and the stub ferrule is engaged with the ferrule of the optical connector. The stub ferrule and the split sleeve are made of ceramic and the sleeve cover and the holder are made of steel.
In the above-mentioned structure, however, problems will arise as follows: (1) Because a large proportion of the structure is accounted for by metal parts, the optical transmitter or receiver tends to work as a radiation transmission antenna or a reception antenna and, as a result, the EMC characteristics deteriorate, and (2) Because a metal and a ceramic are used at the leading end portion of the receptacle where the connector is connected, on account of electrical noise entering from the connector side, the characteristics of the other component parts deteriorate.
On the other hand, in a technology disclosed in JP-A-5-249344, an attempt is made to improve static electricity discharge resistance by forming the receptacle main body by a high insulation material, but no consideration is given to means for solving the problem of electrostatic discharge through the optical connector, nor is any concrete method disclosed for use with a light-emitting device module or light-receiving device module for a receptacle as opposed to the present invention.